Etoile + GNUstep desktop OS environment -- according to how I understand Etoile
project, that doesn't really make sense, since Etoile is a project to develop
an OS (and any components necessary to do so along the way). :-)

Then you misunderstand Étoilé. We are developing a user environment that runs
atop an existing OS, not a new OS.

The same holds for GAP. The name is GNUstep Application Project, not
Operating System. That was SideStep.